The basement membrane (BM) separates epithelial elements from the surrounding stroma. BM is dynamic in regulation of epithelial cells differentiation as well as their organization into 3-dimensional tissues. In these functions, among the molecules of the BM, laminins are especially dynamic. Laminins are distributed in a spatially and temporally regulated manner in various epithelial tissues. Various changes in the laminin distribution accompany the malignant transformation of epithelia. The role of the BM and laminins in the progression of carcinomas is not well understood. The BM has been suggested to act as a mechanical barrier against carcinoma cell invasion. BM laminins may play an active role in regulating the migration and proliferation of the carcinoma cells. Laminin isoform laminin-5 expression is typical for some invasive carcinomas and it may act as a ligand for invading carcinoma cells. Neoexpression of laminin-5 has also been associated to proliferative activity of the carcinoma cells. Integrins ␣ 3  1 and ␣ 6  4 are probable cell surface receptors acting with laminin-5 in the regulation of carcoma cell invasion and proliferation. © 2001 Wiley-Liss, Inc.
Key words: laminin-5; carcinomas; invasion; integrin; basement membranesBasement membrane (BM) is a densified sheet of proteins of the extracellular matrix. The BM separates connective tissue from epithelium. In addition, endothelium, various types of muscle cell, lipocytes and Schwann cells are surrounded by BM. 1 Structural components of the BM are at least laminins, type IV collagens, nidogens, proteoglycans such as perlecan, fibulins as well as type VII collagen in the BMs containing lamina fibroreticularis layer. Additionally, fibronectin and tenascin are often located to the BM region, but they are not the structural components of the BMs. BM molecules are produced in cooperation between epithelial and mesenchymal cells. 2 Collagen type IV is a helical, trimeric protein. The most widely expressed type IV collagen trimer is composed of 2 ␣1(IV) chains and one ␣2(IV) chain. 3 The ␣3(IV)-␣6(IV) chains have a more restricted tissue distribution, present for example in the kidney. 4 -6 Nidogen-1 is a 150 kD glycoprotein consisting of three globular domains. 7 It binds collagen IV and laminin networks together. 8 Nidogen-1 binds also perlecan, fibulin-1 and fibulin-2. 9 Type VII collagen forms the anchoring fibrils and connects the BM lamina densa to the underlying connective tissue at least in BMs of stratified epithelium. 10,11 Type VII collagen binds, laminin-5 and type IV collagen. 12 The functions of BM in offering mechanical support are well known. 1 In addition to mechanical functions, the BM influences for cell proliferation, differentiation, adhesion, migration and gene expression. 13,14 BM acts as a factor in maintaining polarity and organization of epithelial cells 1,13,15,16 and it is an active regulator in epithelial-mesenchymal interactions during epithelial cell development. 17 BM molecules can regulate the activity of growth facto...